System and a Process to Produce Low Ash Clean Coal from High Ash Coal

ABSTRACT

An industrial process for treating coal in a system to lower ash content, the system comprising first and second water storage tanks, a diesel storage tank, a thermic fluid heater, a thermic fluid storage tank, a thermic fluid pump, a heat exchanger, a thermic fluid expansion tank, a N2 gas cylinder, a reactor, a water pump, and a reflux condenser, the process comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidone (NMP) with Ethylenediamine (EDA) solution, (ii) maintaining said slurry in the reactor at a temperature of 150° C. to 220° C. and at a pressure of 1 to 4 gauge (kg/cm) for about 1 to 3 hours, (iii) separating a sample of the slurry by coarse filtration in a filter cloth to obtain a filtrate/extract and a residue, (iv) precipitating the coal in water by adding concentrated extract, and (v) separating the coal by filtration.

FIELD OF THE INVENTION

The present invention generally relates to cleaning of coal with mineral matter finely disseminated in the organic-mass. More particularly, the invention relates to a system and a process to produce low ash clean coal from high ash coal.

BACKGROUND OF THE INVENTION

As coal is a heterogenous mixture of organic and inorganic constituents, solvolysis of coal varies with its constituents. Maturity, and structural characteristics. Since the mineral matter (non-combustible) in Indian coals is very finely disseminated in the organic mass, it is really very difficult to remove this by conventional physical coal washing techniques. Presence of high percentage of near gravity material in coal makes the scope of gravity process limited. Concept of chemical beneficiation comes from the limitation of physical beneficiation processes. Broadly, chemical beneficiation is possible by chemical leaching of mineral matter present in coal or, dissolving organic matter of coal in various organic solvents. This indicates that chemical treatment may be the right approach to overcome the limitation of physical beneficiation methods. A lot of literature is available on chemical beneficiation techniques that employ highly corrosive chemicals (mostly acids and alkalis). Recovery or regeneration of these chemicals is very important to make this technology viable. A parallel approach towards lowering ash could be recovering the premium organic matter from coal by solvent refining. Literature reveals that most of the research work on this subject was carried out with an objective to produce ultra clean coal or super clean coal with ash content less than 0.2% for various high tech end uses. This conventional solvent refining process does not serve the objective of low ash coal requirement of steel industries because of mainly low recovery which makes the process uneconomic especially when such an ultra coal is not absolutely desired at the cost of restricting to low yields.

By way of reference, Indian patent application numbers 1292/KOL/06, 1088/KOL/07, 1336/KOL/20078, 950/KOL/09, 1195/KOL/09, 611/KOL/09 and 1581/KOL/08 are incorporated herein being related to the similar field of technology.

Main advantages of this process are i) ease of recovery of solvent in the main process stream, ii) solvolytic efficiency of recovered solvents as that of fresh solvent, iii) 95-98% recovery of the solvent, iv) improved coking properties of clean coal, and v) availability of industrial organic solvents. However, the operating cost of this process is high because of high cost of solvents and energy requirement in the process. The inventors made an effort to make this process techno-economic initially through lab-scale process by improving the yield upto 50-60% with less than 8% ash content, including reduction in the cost of solvent recovery.

According to the established process in the laboratory, coal, solvent (N-Methyl-2-Pyrrolidone, NMP) and co-solvent (Ethylenediamine, EDA) are mixed thoroughly to produce a coal slurry. The coal slurry is extracted in a known manner which includes coal-solvent mixture. The mixture is separated in a separation unit to produce a coarser fraction and a finer fraction. The finer fraction is fed to an evaporator unit to allow 70 to 80% off solvent recovery. The hot concentrated coal-solvent mixture is then flushed in a precipitation tank to precipitate the coal. In this case, water as an anti:solvent is used. Water separates the solvent from coal and a water-solvent mixture is obtained, which is fed to a distillation unit to separate solvent and anti-solvent. The precipitated coal is separated in a filter. In the process, coal, solvent and co-solvent are taken in a pre defined ratio. Coal to solvent ratio is varied from 1:6 to 1:17 (wt/vol, g/mL, coal to solvent ratios being wt.vol, and solvent to co-solvent ratio are vol/vol). Coal to co-solvent as well as co-solvent ratio is maintained as 1:1 (g/mL).

OBJECTS OF THE INVENTION

It is therefore an object of this invention to propose an industrial process to produce low ash clean coal from high ash coal.

Another object of this invention is to propose a single reactor-based system to produce low ash clean coal from high ash coal.

A further object of this invention is to propose a validation process to establish the efficiency of the inventive system and process to produce low ash clean coal from high ash coal, as compared to the output from the laboratory scale unit.

SUMMARY OF THE INVENTION

According to the invention, a process flow diagram for an industrial plant with a single reactor is proposed. The important equipments constituting the inventive system, are a thermic fluid heater, a reactor, a heat exchanger, a thermic fluid pump, and an inert gas (N₂) cylinder. Some of the associated equipments or vessels comprise a water storage tank, a diesel storage tank, a thermic fluid storage tank, and an expansion tank.

A reflux condenser (12) is used to maintain pressure at a specified condition. The system also consists of about eighteen gate and ball valves, two pressure gauges, at least one temperature gauge, and four temperature transmitters,

Solvents and coal are loaded into the reactor (10) with the help of opening on the reactor top. Sampling system has been provided at the bottom of the reactor (10) to draw the sample as and when required.

According to the invention, there is provided an industrial process for treating coal to lower ash content in a system, the system comprising a first water storage tank, a second water storage tank, a diesel storage thank, a thermic fluid heater, a thermic fluid storage tank, a thermic fluid pump, a heat exchanger, a thermic fluid expansion tank, a N₂ gas cylinder, a reactor, a water pump, and a reflux condenser, the method comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidone (NMP) with Ethylenediamine (EDA), the NMP and EDA ratio varying between 5:1 to 25:1 solution, said slurry containing about 6 to 18 ml of solution per g of coal, (ii) maintaining said slurry in the reactor at a temperature range of 150° C. to 220° C. and at a pressure range of 1 to 4 gauge (kg/cm²) for a period of about 1 to 3 hours, (iii) separating a sample of the slurry by coarse filtration in a filter cloth, (separation cut size being variable depending on the particle size to be treated and the end produce), to obtain a filtrate or extract and a residue, (iv) precipitating the coal in water by adding concentrated extract, and (vi) separating the coal by filtration, said coal having a reduced ash content.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

FIG. 1—shows a block diagram of a system to produce low-ash clean coal from high-ash coal.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the inventive system comprises a first water storage tank (1), a second water storage tank (2), a diesel storage tank (3), a thermic fluid heater (4), a thermic fluid storage tank (5), a thermic fluid pump (6),a heat exchanger (7), a termic fluid expansion tank (8)m a N₂ gas cylinder (9), a reactor (10), a water pump (11), and a reflux condenser (12).

Coal and solvent in a predetermined ratio are loaded into the reactor (10). Nitrogen gas is supplied through the N₂ cylinder (9) for maintaining inert environment. Diesel is supplied to a burner from the diesel storage tank (3). Thermic fluid is supplied into the system from the thermic fluid storage tank (5). Thermic fluid is heated in the thermic fluid heater (4). On heating, the volume of the thermic fluid increases. Thus, the expansion tank (8) is used to store extra thermic fluid. The reactor (10) is heated by the hot thermic fluid, which is pumped by the thermic fluid pump (6). During extraction, a sample is withdrawn through a sample port with the help of valves (V9, V10). On completion of the extraction step, the burner is switched off. To cool down the thermic fluid heater (4), the thermic fluid is passed through the heat exchanger (7). Water is pumped in the heat exchanger (7) through the water pump (11) from one of the first and second water storage tank (1 or 2). The reflux condenser (12) maintains pressure and temperature at a desired level.

The reactor (10) is configured with desired dimension and capacity for example, diameter-630 mm, height-850 mm, conical height-175, capacity about 425 lit. Coal and solvents are loaded into the reactor (10) through valve V7 in a predetermined ratio. Coal to total solvent ratio is varied from 1:6 to 1:18 (wt/vol, g/mL, coal to solvent ratios are wt/vol and solvent: co-solvent ratios are vol/vol wherever mentioned). Co-solvent to solvent ratio is varied from 1:25 to 1:5. Nitrogen gas is purged into the system for maintaining inert environment. Thermic fluid is pumped into the system from the thermic fluid storage tank (5). Thermic fluid is heated in the thermic fluid heater (4) by the diesel fired burner. The reactor (10) is heated by hot thermic fluid through limpet coils. Reactor pressure is being varied from 1 to 4 gauge (kg/cm²). Reactor temperature is varied from 150° C. to 220° C. Extraction is being done for 1 to 3 hr in the reactor.

The sample is withdriwn from the reactor (10) through the sample port at predetermined time intervals. This sample is filtered through a mesh. Filtration step separates the refluxed mix in two parts (i) residue and (ii) filtrate (extracted material with solvents. Residue is washed thoroughly with an anti-solvent (water) for removal of the solvents from the residue. After drying and weighing, these residues are subjected to ash analysis. The filtrate is actually the extract containing very low ash coal. For precipitation, an anti solvent (water) is taken in a container. Concentrated extract is then added in to the water. As these solvents are soluble in water, solvents move to water phase. It resulted in precipitation of solid coal particles. Thus, precipitated coal is then separated from the solvent-water solution through filtration. This step is carried out in a conical flask-funnel arrangement with standard mesh. The residue of this filtration is the low ash clean coal; filtrate consists of water and the solvents. After drying and weighing, the clean coals are subjected to chemical and petro graphical analysis.

The Experimental results are shown in table 1.

TABLE 1 Clean Exper- Feed Feed Operating Clean Coal iment Ash size Pressure Coal Ash Numbers % % kg/cm² yield % Caol:Solvent 1 26 −0.5 2.5 50 7 1:6  2 26 −0.5 2.5 47 7 1:10 3 26 −0.5 1 50 4 1:6  4 26 −0.5 1 48 4.5 1:10

Some of the experimental results are shown in table 1. The feed coal is run-of-mines (ROM) coal having about 26% ash. The feed particle size is −0.5 mm and extraction is done at 2.5 and 1 kg/cm² pressure. Results are shown at two different coal to solvent ratio, 1:6 and 1:10. Clean coal ash is about 7% when pressure is 2.5 kg/cm² and it is about 4% when pressure is 1 kg/cm². Clean coal yield is about 48% and 50% for 1:10 and 1:6 coal to solvent ratio respectively. It is possible to produce less than 8% ash clean coal in the inventive step. With the help of fine filtration even less than 1% ash clean coal can be obtained. This proves that the results contained in the system, are similar to that obtained at laboratory scale. 

1. An industrial process for treating coal in a system to lower ash content, the system comprising a first water storage tank, a second water storage tank, a diesel storage tank, a thermic fluid heater, a thermic fluid storage tank, a thermic fluid pump, a heat exchanger, a thermic fluid expansion tank, a N2 gas cylinder, a reactor, a water pump, and a reflux condenser, the process comprising (i) forming a slurry of coal fines in a N-Methyl-2-pyrrolidone (NMP) with Ethylenediamine (EDA) solution where the NMP and EDA ratio between 5:1 to 25:1, said slurry containing about 6 to 18 ml of solution per g of coal, (ii) maintaining said slurry in the reactor at a temperature range of 150° C. to 220° C. and at a pressure range of 1 to 4 gauge (kg/cm) for a period of about 1 to 3 hours, (iii) separating a sample of the slurry by coarse filtration in a filter cloth to obtain a filtrate or extract and a residue, (iv) precipitating the coal in water by adding concentrated extract, and (v) separating the coal by filtration, said coal having a reduced ash content.
 2. The process as claimed in claim 1, wherein said coal comprises run of mine coal.
 3. The process as claimed in claim 2, wherein the coal particle size in step (i) is 0.5 mm.
 4. The process as claimed in claim 1, wherein said ultra low ash clean coal or super clean coal having an ash content <1% is produced by fine filtration of the extracted solution.
 5. The process as claimed in claim 4, wherein said ultra low ash clean coal or super clean coal having ash content <1% is used to produce graphite, liquid fuels, aromatic polymers, specially chemicals, and carbon materials.
 6. The process as claimed in claim 1, wherein clean coal having ash content <8% is produced by coarse filtration of the extracted solution.
 7. The process as claimed in claim 6, wherein said clean coal having ash content <8% is used for one of coke making, and blast furnace injection in iron and steel industries, and power plants.
 8. The process as claimed in claim 1, wherein said clean coal having ash content <8% is produced in said system at an yield rate of about 50% clean coal.
 9. The process as claimed in claim 1, wherein said clean coal having ash content <8% is produced in said system with a coal to solvent ratio of 1:6 to 1:18.
 10. The process as claimed in claim 1, wherein said clean coal having ash content <8% is produced in said system at a yield rate equivalent to that of a laboratory set-up.
 11. The process as claimed in claim 1, wherein, in step (iii), the separation cut size is dependent on the coal particle size and the desired end product. 